Measured in your browser.
The file is decoded at 48 kHz, the rate the BS.1770 filter is written for, and measured in a background worker by the same code as the loudness checker.
SOLIPSIUM Super resolution audio engine
Free audio tool
Normalize a recording to a loudness target, louder or quieter.
Set a recording to -14, -16 or -23 LUFS, or a target you type, with one gain for the whole file. Loudness and true peak are measured before and after, and you save an MP3 or a WAV.
Drop a recording here
Your browser measures and normalizes it on this device. It stays on your device until you ask for a repair.
MP3, M4A, WAV, FLAC, OGG, Opus and more, up to 30 minutes or 200 MB.
Loudness before and after
| Measure | Original | Normalized |
|---|---|---|
| Loudness | ||
| True peak | ||
| Sample peak |
Loudness is integrated loudness by ITU-R BS.1770, in LUFS. The true peak is the highest point between samples, found at four times the sample rate, in dBTP. The sample peak is the largest sample, in dBFS.
This file has one channel and is measured that way, as the standard does: it reads about 3 LU lower than the same sound in two channels.
The ceiling is -1 dBTP. If the target would push the true peak past it, the gain stops at the ceiling and the page says where the file landed. With the box ticked, a limiter holds the peaks down instead.
Normalized
MP3 files are made with lamejs, a JavaScript port of LAME, under the GNU LGPL. Turning a file into MP3 can move its peaks a little, so measure an MP3 with the loudness checker before you deliver it.
Is the recording itself clear?
Normalizing does not clean the sound. Solipsium's free try is built for speech: the check below looks at your original file in your browser for background noise, hum, clipping, dropouts and muffled sound, and you can hear the first 20 seconds of a voice recording repaired with no account.
Your first 20 seconds
After signing up, drop the same file into the editor to repair all of it.
What Solipsium hears
Make a free account to repair the whole recording
Then drop the same file into the editor. Scans and short repairs are free.
How it works
One gain, measured before and after.
Normalizing to a loudness target moves the whole recording by the same number of decibels, so the balance between its loud and quiet moments stays as it was.
One gain to the target.
The gain is the target minus the measured loudness, so it can make the file louder or quieter. The result is measured the same way, and the Normalized column shows those numbers.
The limiter, if you ask for it.
It turns the sound down around each peak that would pass the ceiling, easing in 5 ms before it and back up within a quarter of a second, by the same amount in every channel. It holds the samples, so the true peak is measured afterwards; if it is still over, the limiter runs again with the samples held lower, up to three times.
Questions
Before you normalize.
Loudness or peak normalization?
Peak normalization moves a file until its largest sample reaches a level, however loud it then sounds. Loudness normalization sets how loud it sounds, measured in LUFS. To raise a quiet file until its loudest peak reaches -1 dBFS, use Make audio louder.
Why could the target not be reached?
The file's loudest peaks would pass -1 dBTP before its loudness reached the target: one loud peak sets how far the whole file can rise. Tick Limit the peaks and press Normalize again; the limiter turns those peaks down so the rest can come up.
Which target should I choose?
Each platform publishes its own target. The loudness checker quotes what ACX, Apple Podcasts and Spotify ask for, as read on October 15, 2026, and says whether a file meets each.
Does it change the sound?
Without the limiter, only the level changes: every sample is multiplied by the same number. The limiter turns the sound down for short moments around the loudest peaks, and the result line says for how long in all and by how much at most. Pushed far, those moments can sound squeezed, so listen before you deliver.
Can I normalize several files alike?
One at a time. Give each file the same target and they come out at the same measured loudness, unless the ceiling stopped one, which its result line says.
Is my file uploaded?
Not to normalize it. Your browser measures and normalizes the file on this device, and Solipsium's check of the recording runs in your browser too. Audio is sent only if you press Repair the first 20 seconds. For a mono or stereo recording of up to five minutes, only its first 20 seconds leave this browser; Solipsium repairs them on its server and deletes them within an hour. A longer file would have to go whole, so the try is offered for it only under 25 MB, and Solipsium keeps just its first 20 seconds.
Hiss came up with the voice?
Raising the level raises any hiss or hum too. The check runs in your browser and lists the background noise, hum and clipping it finds, and for a voice recording you can hear its first 20 seconds repaired.
Check a recording
The check and the 20-second try need no account.